Radiation-emitting devices are used for the treatment of cancerous tumors within patients. The primary goal of treating cancerous tumors with radiation therapy is the complete eradication of the cancerous cells, while the secondary goal is to avoid, to the maximum possible extent, damaging healthy tissue and organs in the vicinity of the tumor. Typically, a radiation therapy device includes a gantry that can be rotated around a horizontal axis of rotation during the delivery of a therapeutic treatment. A particle linear accelerator (“LINAC”) is located within the gantry, and generates a high-energy radiation beam of therapy, such as an electron beam or photon (x-ray) beam. The patient is placed on a treatment table located at the isocenter of the gantry, and the radiation beam is directed toward the tumor or lesion to be treated.
Radiation therapy typically involves a planning stage and a treatment stage. Generally, the planning stage involves acquiring images of a lesion (using, for example an x-ray device) and subsequently using the image(s) to accurately measure the location, size, contour, and number of lesions to be treated. These are used to establish certain treatment plan parameters, such as an isocenter, beam angles, energy, aperture, dose distribution, and other parameters in an attempt to irradiate the lesion while minimizing damage to surrounding healthy tissue.
Imaging is often used by oncologists in determining the treatment parameters of radiation therapy plans such that the prescribed radiation is sufficient to eliminate the cancerous cells and while conforming the shape of the dose distribution to a target volume to the greatest extent possible, thereby sparing healthy tissue from exposure to potentially harmful doses of radiation. To develop a preferred treatment plan, simulations can be performed to design a set of beams which accomplish this goal that calculate the dose at each point in the patient resulting from this set of beams. The dose distribution can be represented, for example, as isodose lines or as three-dimensional isodose surfaces within the patient. The treatment goal is to encompass the lesion and an appropriate safety margin within the 100% isodose surface. The treatment plan is then administered, usually at a later date and over a period of weeks, based on the treatment parameters. One shortcoming of this approach is that the time lapse between treatment planning and treatment delivery allows for changes to the patient's anatomy, thereby potentially rendering the treatment plan sub-optimal. Changes such as lesion movement, growth, organ shifting, or other morphisms can cause healthy tissue to become subject to potentially harmful radiation, and cancerous tissue to extend beyond the boundaries of the original treatment plan.
Once a treatment plan is determined, the patient receives the radiation treatments during a number of sessions (fractions). Treatment often includes significant time lapses between individual fractions and can also span many weeks (e.g., once a day five days a week for four weeks.) Because organs can change location and/or shape from the time of planning to the delivery of the initial fraction, as well as from fraction to fraction, the original segmented, contoured image may no longer accurately represent the lesion being treated. As a result, the treatment plan may no longer be optimal. Three-dimensional imaging modalities that are able to discern soft-tissues are therefore used in the treatment room in order to detect and compensate for organ motion. However, because of the time constraints imposed during the individual fractions, and the lack of a trained physician during the fractions, it may not be possible to generate an updated segmented or contoured image of the lesion. Thus, methods that provide fast, accurate, and reliable images and patient positioning data without requiring a physician's expertise are of great benefit to a radiation technologist administering the radiation treatment.
Therefore, a fast technique to segment organs or structures of interest prior to a medical procedure with minimal user guidance is needed.